The nuclear medicine imaging such as SPECT (Single Photon Emission Tomography) or PET (Positron Emission Tomography) is a technology for imaging comprising injecting radiopharmaceuticals in a human body, acquiring gamma-rays emitted due to decays of radioactive nuclide by a detector, and reconstructing the acquired data to image data. CT and MRI, which are different types of bio-imaging technologies, are used mainly for investigating abnormalities of morphologies of body tissues. On the other hand, the nuclear medicine imaging technologies can be used not only for investigating morphologies, but also for investigating statuses of functions or metabolisms of internal organs or tissues, based on information such as distributions, aggregations, or time-dependent changes of the injected radiopharmaceuticals, i.e., numbers of counts of the gamma-rays acquired by the detector.
One of the application areas of the nuclear medicine imaging technologies is the myocardial perfusion imaging. The myocardial perfusion imaging (MPI) can be practiced by using SPECT. This method uses radiopharmaceuticals having the nature of being ingested into cardiomyocytes in proportion to the amount of blood flow of the coronary artery as a tracer. Such radiopharmaceuticals may be 201TlCl or 99mTc-tetrofosmin. After such tracer is injected to a subject, the SPECT system acquires gamma-rays generated from the tracer and reconstructs images from the acquired gamma-rays. In these images, locations of ischemia can be appeared as dark sites. So it is possible to investigate whether there are ischemia in, e.g., a cardiac muscle, or not. The Investigation of locations of ischemia in a cardiac muscle is very useful for diagnosing of a myocardial infarction (MI) and an angina pectoris (AP), and identifying locations of lesions caused by ischemia. Since the heart is a moving organ, the SPECT acquisition generally involves gating by electrocardiogram (ECG) for acquiring gamma-rays. Such type of SPECT myocardial imaging has been called as an ECG-gated myocardial SPECT imaging. Usually, the cardiac muscle of the left ventricle is a target for imaging in the ECG-gated myocardial SPECT imaging.
One of the technical challenges in the ECG-gated myocardial SPECT imaging is how to identify the myocardial regions in the reconstructed images. One of the solutions is to manually mark contours of region which may correspond to myocardium based on visual observation in each image slice. But this method has a disadvantage of requiring too much time. So there are prior developments of software for extracting contour points of the myocardial region. QGS (Quantitative Gated SPECT) is one of such software. It was developed by Cedars-Sinai Medical Center. Emory Cardiac Toolbox is also one of such software. It was developed by Emory University. pFAST, developed by Sapporo Medical University, is also such software. The applicant of the present application also disclosed sophisticated algorithms for automatic extraction of myocardial contour points in WO2013/047496 and JP patent application No. 2013-062441.
Prior art document: WO2013/047496